This invention relates to a thermally releasable flavor source for use in smoking articles which produce substantially no smoke. More particularly, this invention relates to a gel-based tobacco-containing thermally releasable flavor source that provides the sensations associated with the smoking of tobacco without the burning of tobacco.
It is known to provide a smoking article in which a flavor source of tobacco, or tobacco-derived material, is heated, without combustion of tobacco, to release tobacco flavors without producing all the normal products of tobacco combustion. For example, U.S. Pat. No. 4,991,606, commonly assigned herewith, describes a smoking article having a source of tobacco-derived material in radiative and convective contact with a combustible heat source. A smoker draws heated air through or around the flavor source, releasing tobacco flavors that are drawn into the smoker's mouth.
In the type of smoking articles described above, it is desirable that the flavor source is easy to manufacture and that it can be easily incorporated into a smoking article. Furthermore, the types of constituents that can be incorporated into the flavor source itself should not be limited. The flavor source should be able to contain any material that releases desirable flavors and other compounds when subjected to a heat source, either by way of conduction, convection, or radiation, or a combination of these. The flavors and other compounds should include those associated with tobacco, or tobacco substitutes, as well as other desirable flavors. The flavor source should also be able to contain a large amount of aerosol precursor that forms an aerosol upon being subjected to heat.
There have been various attempts to produce a flavor source which fulfills the above-described requirements and which provides the smoker with the taste and satisfaction that has become expected of a conventional tobacco-burning smoking article. For example, published European patent application No. 0 212 234 by Banerjee et al. describes a flavor source for use in a smoking article that may comprise granules formed from a mixture of thermally stable adsorbent carbon and tobacco. The granules can also be formed from other thermally stable materials such as alumina. The substrates may be formed in a one step process (e.g., as described in U.S. Pat. No. 27,214) in a "Marumerizer"-type machine and are impregnated with aerosol-forming materials and volatile flavoring agents.
Published European patent application 0 254 848 by Banerjee et al. describes a flavor source where the substrate material used as a carrier, e.g., alumina, porous grade or activated carbons, has been treated so that it has a decreased aerosol retentive capacity, and therefore is capable of producing larger quantities of aerosol upon subjecting the flavor source to heat. The improvement in the production of aerosol is achieved by subjecting the granular substrate materials to high-temperature processing and other steps prior to impregnation.
Nichols et al. U.S. Pat. No. 4,981,522, commonly assigned herewith, describes a flavor source comprising a mixture of tobacco particles, an aerosol precursor, and a filler material that absorbs and radiates heat to minimize the likelihood that the flavor material will ignite. Pellets of the mixture could be formed by extrusion through a die. The amount of aerosol precursor that could be incorporated into the flavor source was indicated to be from about 5 to 35 weight percent.
In prior art articles the amount of aerosol precursor that could be incorporated into the flavor source was limited. It would be desirable to be able to incorporate larger amounts of aerosol precursor and other liquids into the flavor source. Also, as the concentration of these constituents goes up, less heat would be wasted heating a non-aerosol material. Furthermore, the problem of ashing of the flavor source would then inherently be reduced because of the higher concentration levels. Ashing results when liquid is depleted from the part of the flavor source that is closest to the heat source, thereby raising the temperature of this end of the flavor source. Therefore, if the concentration of liquids in the flavor source is increased, this would reduce the possibility of ignition and combustion of the flavor source. Achievement of such a reduction in ashing would also allow the heat source to be positioned closer to the flavor source in a smoking article.
Accordingly, it would be desirable to have a flavor source capable of containing higher concentrations of aerosol precursors and other liquids so as to have the added advantages of reducing the ashing tendency of the prior art smoking articles.
In prior art articles the flavor source was generally comprised of a packed-bed of individual aerosol-generating pellets or particles. This resulted in a smoking article that was comprised of a large number of parts, which renders its manufacture difficult. In particular, the packed bed had to be held in place by a screen-like clip which allowed the aerosol to pass through it into an expansion chamber.
Accordingly, it would be desirable to eliminate the need for a packed-bed of individual pellets or particles as well as the manufacturing complexity associated with such a packed bed. Furthermore, it would be desirable to have a one-piece flavor source which can simply be inserted into a smoking article without the need for any screen-like clips.
Such a one-piece flavor source would also have the added advantage of reducing inconsistencies in flavor delivery to the user. With packed-bed flavor sources the consistency in flavor delivery depends upon the consistency in flavor bed loading, in addition to the consistency of the physical and chemical characteristics of the individual pellets or particles. It would be desirable to be able to provide a one-piece flavor source so as to improve the consistency of flavor delivery to the user.